1. Field of the Invention
The present invention relates to an ink-jet recording apparatus and an ink-jet recording method. More particularly, the invention relates to an ink-jet recording apparatus and an ink-jet recording method performing multi-pass recording in which an image is formed by executing a plurality of runs of main scanning moving a recording head discharging ink a plurality of times relative to a recording medium for the individual recording areas on the recording medium.
2. Description of the Related Art
A recording apparatus such as a printer, copying machine, or facsimile machine; or a composite type electronic device such as a computer or a wordprocessor; or a recording apparatus used as an output device such as a workstation, has a configuration to permit recording onto a recording medium such as a sheet of paper or a plastic sheet on the basis of the image information including character information and the like.
These recording apparatuses can be classified, in terms of their recording method, into ink-jet, wire-dot, thermal and laser beam recording apparatuses. From among these recording apparatuses, the ink-jet type of recording apparatus (ink-jet recording apparatus) accomplishes recording by discharging ink from a recording means such as a recording head onto a recording medium, and has excellent features of easy refinement, high speed, quietness, and low cost.
On the other hand, there is an increasing demand for color recording, and many color ink-jet recording apparatuses have been developed. The ink-jet recording apparatus uses a recording head comprising a plurality of ink discharge ports and liquid paths for ink discharge to improve the recording speed, and generally has a plurality of recording heads.
FIG. 1 illustrates a schematic configuration of a general printer section of the type in which recording is performed by causing a recording head to scan a plurality of times a sheet of recording paper P. In FIG. 1, reference numeral 101 represents four different ink cartridges. Each of the four cartridges comprises an ink tank containing either black, cyan, magenta or yellow ink, and a recording head 102.
FIG. 2 illustrates a cross-sectional view of a discharge port provided in each recording head, as viewed from the z-direction. As shown in FIG. 2, a plurality of discharge ports 201 are arranged at prescribed intervals on the recording head 102.
Referring again to FIG. 1, reference numeral 103 represents a paper feeding roller, which rotates in the arrow direction in FIG. 1 while pressing sheets of recording paper P, together with an auxiliary roller 104, thus feeding the recording paper P from time to time in the y-direction; reference numeral 105, a pair of paper feeding roller, also feed recording paper and plays a role of pressing the recording paper P, similar to the paper feeding roller 103 and the auxiliary roller 104; and reference numeral 106, a carriage, supports the four ink cartridges 101 and causes them to move and scan upon recording. When recording is not conducted, or when carrying out a recovery operation of the recording head, the four ink cartridges are waiting at a home position (h), as shown by the dotted line in FIG. 1.
Before starting recording, and upon receipt of a recording start command, the carriage 106 at the home position in FIG. 1 discharges ink from a plurality of discharge ports 201 (shown in FIG. 2) on the recording head 102 while moving in an x-direction for recording. When the recording of data at the end of the paper is completed, the carriage 106 returns to the home position h, and performs recording again in the x-direction.
When recording an image or the like, various factors including the properties of each color, gradation and uniformity need to be considered. In particular, with regard to uniformity, it is known that a slight variation between nozzles produced during the recording head manufacturing process exerts an influence on the ink discharge amount of each nozzle or the direction of ink discharge upon recording, leads to deterioration of the image quality as a density irregularity of the recorded image.
A concrete example of this density irregularity will be provided, with reference to FIGS. 3 and 4. In FIG. 3A, reference numeral 31 represents a recording head comprising eight nozzles 32; and reference numeral 33 represents ink drops discharged by the nozzles 32, which should ideally be discharged in uniform amounts and in a uniform direction, as shown in FIG. 3. When such a discharge is achieved, dots of a uniform size are dropped, as shown in FIG. 3B, and a uniform image, free from density irregularity as a whole, is obtained (as shown in FIG. 3C).
However, nozzles are not uniform as described above. If recording is conducted with these nozzles as they are, variations in size and the irregular direction of ink drops discharged from the individual nozzles occurs, as shown in FIG. 4A, and the ink drops reach the recording medium in a non-uniform manner as shown in FIG. 4B. According to FIG. 4B, blank portions, which cannot fully satisfy an area factor of 100%, are present periodically in the head""s main scanning direction, or dots overlap, or a white line, as observed at the center of FIG. 4B is produced.
A collection of dots deposited in the state as described above (as shown in FIG. 4B) takes a density distribution, as shown in FIG. 4C, and finally, as viewed by ordinary human eyes, these phenomena are sensed as density irregularities. Apart from this, when there are variations in the paper feed amount, lines may become apparent in the recorded image.
To avoid such density irregularities, U.S. Pat. No. 5,696,542 discloses the following method, which will briefly be described with reference to FIGS. 4 and 5. According to this method, three runs of main scanning of a recording head 31 are conducted (FIG. 5A) to complete a recording area shown in FIG. 5B, and a unit area of four pixels accounting for half of the recording area is completed with two passes. In this case, eight nozzles of the recording head are divided into two groups including four upper nozzles and four lower nozzles. Dots recorded in a single run of main scanning by a nozzle are those resulting from a prescribed image data thinned to about a half in accordance with a prescribed image data arrangement (printed pattern). During the second run of main scanning, the remaining half of the dots are embedded in the printed medium to complete the recording of a unit area of four pixels. This recording method is hereinafter referred to as the multi-pass recording method.
According to such a recording method, even when using a head equivalent to the recording head shown in FIG. 4, the effect of variations intrinsic to the individual nozzles on the recorded image is reduced by half, resulting in a recorded image as shown in FIG. 5B, the black and white lines observed in FIG. 4B are not very conspicuous. Therefore, the density irregularities are alleviated to a large extent as compared with the case shown in FIG. 4C, as shown in FIG. 5C.
When conducting such multi-pass recording, in the first and second runs of main scanning, image data are divided in a mutually compensating form in accordance with a prescribed printed pattern. For this printed pattern, it is common to use one printed pattern that results in a checkers pattern for each pixel horizontally and vertically formed. This printed pattern is hereinafter referred to as the checkers pattern. By using such a printed pattern, in a unit recording area (in units of four pixels in this case), recording is completed by the first run of main scanning for recording the checkers pattern and the second run of main scanning for recording the reverse checkers pattern. The checkers pattern used in the second run of main scanning is just the reverse of the checkers pattern used in the first run of main scanning.
FIGS. 6A, 6B, and 6C illustrate how recording on a certain area is worked out when using the checkers and the reverse checkers printed patterns. In FIG. 6A, printed patterns are shown with checkers pattern A and checkers pattern B, and the pattern B is just the reverse of the pattern A. In the first run of main scanning in FIG. 6A, recording is carried out with the checkers printed pattern by using the four lower nozzles (FIG. 6A). Then, in the second run of main scanning, paper is fed by four pixels (xc2xd head length), and recording is performed with the reverse checkers printed pattern (shown in FIG. 6B). In the third run of main scanning, paper is fed again by four pixels (xc2xd head length), and recording is effected again with the checkers printed pattern (shown in FIG. 6C). A unit recording area of four pixels is thus completed in each run of main scanning by sequentially and alternately applying paper feeding by four pixels as a unit, and by the recording of checkers and reverse checkers printed patterns.
As described above, a high-quality image free from density irregularity can be obtained by completing an image in each recording area with two kinds of nozzles.
A technique of recording a high-quality image free from density irregularity or color unevenness by ensuring a time for ink penetration and fixing into a recording medium is disclosed in Japanese Patent Laid-Open No. 07-47695. The method will be briefly described as follows. The recording of a high-quality image free from density irregularity or color unevenness is achieved by recording a line to be recorded by reciprocal record scanning of a recording head, and keeping the recording head waiting for a prescribed waiting time at a position where the recording head stops between the forward and backward runs of the scanning head.
However, Japanese Patent Laid-Open No. 07-47695 does not teach or support a method where an image is completed by multi-pass recording, and it is unknown whether or not an effect is available by applying the technique of that Laid-Open Publication to the multi-pass recording method.
The present inventors carried out experiments of the multi-pass recording method and discontinues recording for a prescribed period of time for each run of record scanning, and noted the number of runs of record scanning to complete an image, density irregularity, color unevenness, blotting between colors, and staining of the recording medium caused by contact between the recording head and the recording medium. As a result, the inventors obtained the following findings. As the number of runs of record scanning increases, density irregularity, color unevenness and blotting between colors are reduced, and the staining of the recording medium becomes more serious.
These phenomena are attributable to the fact that the multi-pass recording method can prevent density irregularities, and on the other hand, that an increased number of runs of record scanning corresponds to a smaller number of dots recorded per unit time and per unit area, and this leads to a change in penetration or fixing status into the recording medium. Accordingly, as an increased number of runs of record scanning are required for completing the image areas and more time is required before the completion of an image, a phenomenon known as cockling, in which waves are produced in the recording medium (particularly ordinary-paper-based recording medium), becomes more serious, and the contact between the recording head and the recording medium causes more serious staining of the recording medium.
The present invention was developed in view of the above-mentioned circumstances, and has an object to provide an ink-jet recording apparatus and an ink-jet recording method which ensure a time for penetration and fixing of ink into the recording medium, and permit recording of a high-quality image by preventing density irregularity, color unevenness, blotting between colors, and staining of the recording medium caused by contact between the recording head and the recording medium.
To achieve the aforementioned object, the present invention provides an ink-jet recording apparatus comprising: main scanning means for performing main scanning, which moves a recording head discharging ink above a recording medium, and conducts recording by discharging the ink from the recording head onto the recording medium; recording controlling means for executing a plurality of runs of main scanning of the recording head by the main scanning means to a recording area of the recording medium, and for performing multi-pass recording, which completes an image on the recording area; recording mode setting means, which sets a recording mode from a plurality of recording modes with a different number of runs of the main scanning by the multi-pass recording to the recording area; and rest period setting means, which sets a rest period during which recording is discontinued after the individual runs of main scanning in the multi-pass recording.
The ink-jet recording method of the present invention, which carries out main scanning by moving a recording head discharging ink above a recording medium, and conducts recording onto the recording medium by discharging the ink from the recording head comprising: a recording mode selecting step of selecting a recording mode from a plurality of recording modes of a different number of runs of the main scanning for the recording and when performing multi-pass recording, which completes an image for the recording area, by applying a plurality of runs of the main scanning to the recording area of the recording medium; a rest period setting step of setting a rest period during which recording is discontinued after each run of main scanning in the multi-pass recording in response to the number of runs of main scanning corresponding to the selected recording mode; and a step of conducting recording in response to the selected recording mode.
More specifically, in the present invention, when performing multi-pass recording of executing a plurality of runs of main scanning, for each recording area in which the recording head discharging the ink to the recording medium is moved relatively, a plurality of recording modes of a different number of runs of main scanning is provided for each recording area, and a rest period during which recording is discontinued after a run of main scanning is set in response to the number of runs of main scanning of the recording mode.
In this case, the rest period for a recording mode setting forth more runs of main scanning should preferably be shorter than the rest period for a recording mode setting forth a fewer runs of main scanning.
By doing as described above, in multi-pass recording, it is possible to set a rest period, taking into account the amount of ink discharged per unit time or per unit area, the response to the number of runs of main scanning to each area, and the time required for completing the recording.
It is therefore possible to record a high-quality image by ensuring a time for penetration and fixing of ink into the recording medium, and preventing density irregularity, color unevenness, blotting between colors, and staining of the recording medium caused by contact between the recording head and the recording medium.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.